One Rep Max Calculator (Epley Formula)

About the One Rep Max Calculator (Epley Formula)

The Epley formula is one of the most common ways to estimate a one-rep max from a submaximal set.

Instead of testing a true max, you can use a moderate rep set to build a working estimate for percentage-based programming. Epley is widely used because it is simple and tends to work reasonably well in lower to moderate rep ranges.

This calculator applies the formula, generates a percentage chart, and shows corresponding training weights.

When This Page Helps

It is useful when you want percentage-based training weights without taking a maximal attempt. The estimate is best treated as a programming reference, especially when the source set is kept in a moderate rep range.

How to Use the Inputs

1. Perform a set of an exercise to near failure (2–10 reps is most accurate).
2. Enter the weight you lifted.
3. Enter the number of reps completed with good form.
4. View your estimated 1RM and the percentage breakdown chart.
5. Use the percentage chart to set weights for your training program.

Example Calculation

Tips & Best Practices

• Use 2–10 reps for the most accurate estimate. The Epley formula becomes less reliable above 10 reps.
• Perform the set with good form and controlled tempo. Cheating reps will inflate the estimate.
• Test with compound movements (bench, squat, deadlift) for the most useful training data.
• Retest every 4–6 weeks as your training progresses to update working weights.
• Compare results with the Brzycki formula — if both agree closely, your estimate is likely accurate.
• Never actually attempt a calculated 1RM cold. Always work up gradually with proper warm-up sets.

History of the Epley Formula

Boyd Epley developed his formula while serving as strength coach at the University of Nebraska in the 1980s. He needed a practical way to set training weights for football players without the time and injury risk of constant maximal testing. The formula's simplicity (just multiply by 1 + reps/30) made it easy for coaches to calculate on the fly, even without a calculator.

When to Retest Your Max

Retest every 4–6 weeks during a linear progression program, or at the start of each new training block in a periodized program. If your training weights feel significantly easier or harder than prescribed RPE, your estimated max may have shifted and should be retested. Avoid retesting during deload weeks or when fatigued from high-volume training.

Percentage Chart Training Goals

The percentage chart is a simple reference for setting loads. For powerlifting peaking: work from 70% up to 95–100% over 8–12 weeks. For bodybuilding: stay primarily at 65–80% with higher volume. For athletic performance: use 75–85% with explosive intent. Treat the chart as a starting framework and adjust based on actual performance.

Frequently Asked Questions

• How accurate is the Epley formula?

  Studies show the Epley formula is typically within 5–10% of actual 1RM for trained individuals in the 2–10 rep range. Accuracy decreases above 10 reps, where it tends to overestimate. Individual variation exists — some people's rep-max relationship is naturally different from the formula's prediction.

• Why does Epley overestimate at high reps?

  At high reps (12+), fatigue increasingly becomes a cardiovascular and muscular endurance challenge rather than a pure strength limitation. The Epley formula assumes a linear relationship between reps and max strength, but at higher reps, other factors (lactic acid, glycogen depletion, mental fatigue) limit performance before true maximal strength is reached.

• Should I use Epley or Brzycki?

  For 1–6 reps, both formulas give very similar results. For 7–10 reps, Brzycki tends to give slightly lower (more conservative) estimates. Most coaches recommend using the average of multiple formulas for the best accuracy. Our multi-formula calculator does this automatically.

• Can I use this for any exercise?

  The formula works best for compound barbell movements (bench press, squat, deadlift, overhead press). It's less accurate for isolation exercises, machine movements, and exercises with variable resistance. It was originally developed and validated for barbell exercises.

• How should I train based on my estimated 1RM?

  Common programming guidelines: Strength — 3–5 reps at 85–95% 1RM. Hypertrophy — 6–12 reps at 65–80% 1RM. Muscular endurance — 12–20 reps at 50–65% 1RM. Power — 1–3 reps at 80–90% 1RM with explosive tempo. These are starting points; adjust based on individual response.

• Do I need to go to failure to get an accurate estimate?

  You should go close to failure (within 1–2 reps of failure, called RPE 8–9) but not to absolute technical failure. Stopping 1 rep short gives a very similar estimate while being safer. If you stop 2–3 reps before failure, you'll underestimate your 1RM.